The Collaborative International Dictionary of English v.0.48:

Sexagenary \Sex*ag"e*na*ry\, a. [L. sexagenarius, fr. sexageni
   sixty each, akin to sexaginta sixty, sex six: cf.
   sexag['e]naire. See Six.]
   Pertaining to, or designating, the number sixty; poceeding by
   sixties; sixty years old.
   [1913 Webster]

   Sexagenary arithmetic. See under Sexagesimal.

   Sexagenary scale, or Sexagesimal scale (Math.), a scale
      of numbers in which the modulus is sixty. It is used in
      treating the divisions of the circle.
      [1913 Webster]